(1) Field of the Invention
The present invention relates to a technique preferably executing a combustion control at a time of a premixed combustion mode in a control apparatus of an engine having a premixed combustion mode.
(2) Description of Related Art
In a diesel engine, there is considered to employ a premixed combustion mode which burns an air-fuel mixture in a state of premixing the air-fuel mixture as much as possible, and reduces NOx. In order to establish the combustion, a premixed gas is formed by finishing a fuel injection as early as possible in an intake stroke or a compression stroke. On the other hand, in the light of a combustion slapping sound generation due to a sharp ascent of a cylinder internal pressure, ensuring a combustion control robustness or the like, there is considered a method of achieving a premixed combustion mode by introducing a lot of EGR at a time of a low load, and ensuring an ignition lag time on the basis of an intake of an inert gas. At this time, since an EGR rate becomes relatively larger in comparison with a normal diffusion combustion mode time, it is necessary to precisely control an EGR flow rate at a time of the premixed combustion mode or at a time of switching to the premixed combustion mode from the diffusion combustion mode. For example, in patent document 1 (JP-A-2003-286880), there is disclosed a technique which estimates an EGR rate within a cylinder from an oxygen concentration or the like determined on the basis of a signal of an air flow sensor installed in an upstream side of an intake pipe and a signal of a linear O2 sensor installed in an exhaust pipe, and is applied to a control at the time of switching the combustion, in a diesel engine switching a premixed combustion and a diffusion combustion in accordance with the EGR rate.
However, in the invention described in the publication mentioned above, the following problems are generated. In other words, in the engine, since a portion from the installed place of the air flow sensor to the combustion chamber is long, and a volume (a dead volume) equal to or more than a fixed level is provided, a displacement is generated between an EGR amount determined on the basis of a detected air amount and an EGR amount actually sucked into the engine, at a transition time such as a rapid acceleration or deceleration. Further, in a diesel engine using a supercharger, since the supercharger and an intercooler are provided, the displacement is further increased.
Further, an exhaust air sensor such as a linear O2 or the like has a problem in view of a response, and it is hard to feed back a combustion state at several cycles. In other words, in the case that it is necessary to precisely control an ignition combustion at each of the cycles, there is required a new technique for stabilizing the combustion and preventing the exhaust gas (NOx, soot) deterioration, particularly in the transient state or the like.